The present invention relates to an apparatus for applying coatings and in particular to a vacuum coating apparatus.
A vacuum coating apparatus is known e.g. from V.A. Osipov et al. (Journal of Experimental Instruments and Methods, No.6, 1978, pages. 173-176.) The apparatus comprises a vacuum chamber having a housing used as an anode, a cathode, an arc power supply, an evaporator solenoid and chamber solenoids. Vacuum arc deposition of coatings is effected in the chamber with separation of streams of charged and neutral particles.
The apparatus, however, suffers low efficiency and does not provide high-quality coatings because the stream of deposited particles contains a large proportion of macroparticles reflected from the surface of the inner walls of the vacuum chamber.
The closest prior art is a vacuum coating apparatus comprising a consumable metal cathode accommodated in a housing used as an anode, a solenoid mounted on the anode, the anode being in communication with and electrically coupled to a vacuum chamber, and connected to an arc discharge dc power supply, the consumable metal cathode being connected to the arc discharge dc power supply, and a capacitor with a ballasting resistor shunted to the arc discharge dc power supply. The apparatus further comprises an arc striking system including a starter electrode and a dielectric insert (see e.g. Aksenov I. I. et al. Journal of Experimental Instruments and Methods, No. 3, 1979, pages 160-162).
The apparatus, however, does not permit producing coatings with a high-quality surface, i.e. having a low degree of roughness, because the products of cathode erosion in the vacuum arc discharge contain a large proportion of drops and macroparticles which, being deposited onto the substrate surface, form micro-protrusions and pinholes in the coating, thus impairing its quality. Further, the employed arc striking system requires the application of high voltages (4.5 kV) and is insufficiently reliable. A supplemental anode adds complexity to the structure, as it is located in the immediate vicinity of the cathode with a gap. Due to internal stresses the macroparticles detaching from the cathode in the deposition process may fill the gap, thus providing an electrical short.
The object of the present invention is to provide a vacuum coating apparatus to produce high quality coatings with a low degree of roughness and a high degree of thickness uniformity. The vacuum coating apparatus of the invention comprises a consumable metal cathode coupled to an arc discharge power supply and accommodated in a housing used as an anode, which is electrically coupled to a vacuum chamber and connected to the arc discharge dc power supply, a solenoid disposed on the anode, and an arc striking system connected to an initiation unit.
Another feature of the invention is an eccentric offset of the axis of the consumable metal cathode and the anode relative to the axis of the main solenoid.
Another feature of the invention is the placement of the substrate to be coated in a region outside the cathode visibility area, where the substrate is oriented such that its surface is normal to the axis of the solenoid.
Another feature of the invention is the provision of ribs of a predetermined shape on a part of the inner surface of the anode and a design of the arc striking system to prevent the reflection of macroparticles of the deposited coating toward the substrate of the article to be coated.
Another feature of the invention is that the apparatus advantageously comprises at least one deflecting solenoid to further deflect lines of force of the magnetic field generated by the main solenoid and a supplemental solenoid in the direction of the substrate to be coated, the deflecting solenoid being disposed on the vacuum chamber.
Another feature of the invention is that the apparatus and the striking circuit are simple in design and exhibit enhanced reliability.
The present invention is suitable for producing coatings based on metals, such as titanium, aluminum, chromium, zirconium, etc., as well as for depositing wear-resistant coatings based on compounds of the above metals, e.g. titanium nitride, aluminum nitride, chromium nitride, zirconium nitride, etc. The coatings may be used to improve life and operating performance of tools and machine parts, and as decorative coatings.